A Mechanical Ventilation with Heat Recovery (MVHR) system can offer many benefits, including improved indoor air quality and energy efficiency. However, there are situations where an MVHR system might be most suitable. Here are some scenarios:
1. Airtight Buildings
MVHR systems are most effective in buildings with a high level of airtightness. If a building is leaky and not well-sealed, the system may not perform efficiently because too much unfiltered air can enter through gaps and cracks, bypassing the MVHR system. As a general rule, here is a chart giving the effectiveness of MVHR heat recovery vs. the air permeability test/air leakage rate of the home.
|
q50 Result (m³/h.m²
@50Pa
)
|
Suitability for MVHR
|
Rationale
|
|---|---|---|
|
>10
|
Not recommended
|
High leakage mimics natural ventilation; MVHR adds unnecessary cost/energy use without heat recovery gains. (Regulatory max, but poor for efficiency.)
|
|
5–10
|
Marginal benefits
|
Some savings possible, but infiltration may exceed MVHR's controlled rate (e.g., 0.3-0.5 ACH), diluting heat recovery. Suitable for retrofits.
|
|
≤5
|
Good benefits
|
Infiltration drops below typical MVHR supply rate (~0.3 ACH); system dominates ventilation, recovering 80-90% heat. Recommended threshold by most manufacturers.
|
|
≤3
|
Optimal benefits
|
Minimal leakage (~0.1 ACH); maximises energy savings (up to 10% CO₂ reduction), air quality, and payback (2-5 years). Aligns with near-Passivhaus standards.
|
|
<1
|
Exceptional (Passivhaus)
|
Ultra-low leakage; MVHR essential for ventilation, with near-total heat recovery.
|
2. High Energy Efficiency Goals
For homes aiming for low-energy or Passivhaus standards (q50 ≤ 3 or even < 1 m³/h.m²), MVHR is a game-changer. By recovering heat that would otherwise be lost, it can reduce heating costs by up to 20%, making it essential for eco-conscious designs.
3. Poor Natural Ventilation Potential
Homes in urban settings or with limited window access (e.g., flats or terraced houses) benefit from MVHR’s consistent supply of filtered fresh air. It eliminates reliance on opening windows, which may be impractical or ineffective or give rise to security issues.
4. Noise-Sensitive Locations
In noisy areas, such as near busy roads or airports, MVHR allows windows to remain closed while delivering fresh air. This reduces external noise intrusion compared to natural ventilation, enhancing comfort.
5. New Builds or Major Retrofits
Installing MVHR is most cost-effective during new construction or deep retrofits. Ducting can be seamlessly integrated, and builders can ensure airtightness (q50 ≤ 5) to optimise the system’s performance from the start.
6. Regulatory Compliance (Part L)
Apart from being a route to compliance for Part F Ventilation Regs, MVHR helps meet UK Building Regulations Part L by minimising ventilation-related heat loss in airtight homes (q50 ≤ 5). It supports low-carbon goals and can improve Energy Performance Certificate (EPC) ratings, adding value to the property. In some instances, it can also be used for achieving the requirements of Approved Document O, Overheating.
7. Cold or Temperate Climates
The UK’s cool climate makes MVHR a smart choice. Unlike natural ventilation, which loses heat through open windows or leaks, MVHR retains warmth while ensuring fresh air, keeping homes comfortable and energy bills low year-round.
8. Securing Planning Permission
Incorporating MVHR into a planning application for a new build, extension, or conversion in the UK can significantly aid in achieving compliance with SAP (Standard Assessment Procedure) calculations and securing Building Regulations approval (often referred to as "building approval").
While MVHR is not always mandatory, it plays a pivotal role in meeting the energy efficiency and ventilation standards under Part L(Conservation of Fuel and Power) and Part F Ventilation of the Building Regulations. This can strengthen your planning submission by demonstrating sustainability, reducing carbon emissions, and aligning with local authority policies on low-carbon development.
Careful consideration and a professional assessment are recommended to determine if an MVHR system is the right choice for a particular situation. So if you would like some advice, please either call 01892 600121 or email us on MVHR@epicair.co.uk and our experts will be delighted to help.
In the meantime, if you'd like to understand more about MVHR, why not check out our blog What is MVHR and how does it work.
